Identify and obtain lymphocyte homozygous typing cells to the D locus to aid research in cell characterization. Provide NIAID Reagent Bank lymphocytes from a minimum of ten donors approved by the Project Officer as the basis of data showing homozygosity at the D locus. These homozygous typing cells (HTC) will be deposited in the NIAID HLA repository for distribution to other investigators. Serve as a quality control laboratory to verify results of other participating contractors.